We propose to continue a study in which 17 hyperactive children have been tested so far. In this work, the two acute dosages of methylphenidate (0.3 and 0.6 mg/Kg) are compared with placebo concerning their effects on vigilance performance and brain evoked responses. Two of the procedures are drawn from our previous research and two from other laboratories. We plan to bring the sample size to 30 patients. In addition, we propose to conduct a study testing the effects of 0.3 mg/Kg methylphenidate and placebo on young adults' evoked potentials during a long vigilance task (30 minutes). This work is intended to extend our previous finding of parallel drug effects on children and young adults', i.e. enhancement of performance and amplitude of the late positive component of the evoked response. The extension of the vigil should maximize these pharmacologic effects.